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15 Summary of form & texture perception coding of spatial features Evidences of SA1 specialization for the representation of spatial information: SA1 responses to stimulus elements on a surface are independent of the force of application. SA1-receptive fields grow minimally (relative to RA receptive fields) with increasing indentation depth. SA1 afferents possess a response property, surround suppression, which confers response properties similar to those produced by surround inhibition in the central nervous system. This response property is a consequence of sensitivity to strain energy density, not a synaptic mechanism. SA1 spatial resolution is affected minimally by changes in scanning velocity at velocities up to at least 80 mm s–1. SA1 afferents are at least ten times more sensitive to dynamic than to static stimuli. SA1 responses to repeated skin indentation are practically invariant: the variability is about one impulse per trial regardless of the number of action potentials evoked. The RA system has greater sensitivity but poorer spatial resolution and limited dynamic range.

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20 P channel intense filtering (at nearly 60 dB per decade) of low-frequency stimuli respond to stimuli less than 100–150 Hz with a phase-locked, Poisson discharge, therefore a whole population firing randomly but at a rate proportional to the instantaneous stimulus amplitude can represent the stimulus waveform accurately RA channel RA neurons of S1, like their afferent fibers, fire periodically, in phase with mechanical oscillations RA neurons modulate their firing rates as a function of the stimulus frequency Flutter is encoded by firing rate of RA neurons Summary of vibrotactile perception - coding of temporal features